Self-reported knee joint instability is related to passive mechanical stiffness in medial knee osteoarthritis

Abstract

Background: Self-reported knee joint instability compromises function in individuals with medial knee osteoarthritis and may be related to impaired joint mechanics. The purpose of this study was to evaluate the relationship between self-reported instability and the passive varus-valgus mechanical behaviour of the medial osteoarthritis knee.

Methods: Passive varus-valgus angular laxity and stiffness were assessed using a modified isokinetic dynamometer in 73 participants with medial tibiofemoral osteoarthritis. All participants self-reported the absence or presence of knee instability symptoms and the degree to which instability affected daily activity on a 6-point likert scale.

Results: Forward linear regression modelling identified a significant inverse relationship between passive mid-range knee stiffness and symptoms of knee instability (r = 0.27; P < 0.05): reduced stiffness was indicative of more severe instability symptoms. Angular laxity and end-range stiffness were not related to instability symptoms (P > 0.05).

Conclusions: Conceivably, a stiffer passive system may contribute toward greater joint stability during functional activities. Importantly however, net joint stiffness is influenced by both active and passive stiffness, and thus the active neuromuscular system may compensate for reduced passive stiffness in order to maintain joint stability. Future work is merited to examine the role of active stiffness in symptomatic joint stability.

Figure 1

Experimental setup for the evaluation of passive knee varus-valgus laxity and stiffness.

Figure 2

Net moment-angle curves for two study participants are depicted. One participant reported no symptoms of instability (solid green line), the other participant reported that instability severely affected activity (dashed blue line). Mid-range passive stiffness, as indicated by the gradient of the thickened portion of the lines, is noticeably greater in the participant with no symptoms of instability, yet total range-of-motion is similar in both participants.